One known apparatus for regulating the temperature in the cabin of a vehicle makes use of an air conditioning apparatus in which a refrigerant fluid flows in one direction between an evaporator, in which it receives heat from an air stream, and a condenser in which it yields heat to an air stream. In this known type of apparatus, when it is required to cool an air stream before delivering it into the cabin of the vehicle, it is brought into contact with the evaporator. On the other hand, when it is required to heat an air stream before delivering it into the cabin, use is commonly made for this purpose of the heat which is given off by the internal combustion propulsion engine of the vehicle.
In the case of an electric vehicle, the heat which is produced by the electrical propulsion system is not enough to satisfy the heating requirements of the cabin under severe weather conditions in winter. It is therefore necessary to provide an auxiliary source of heat.